1. Field of the Invention
The present invention generally relates to a polyester composition for films and, ore particularly, to a polyester composition suitable for films excellent in abrasion resistance and slipping property without formation of large projections
2. Description of the Related Art
Generally, thermoplastic polyesters, for example, polyethylene terephthalate have excellent physical and chemical properties and are broadly used as fiber, film and other formed articles. Among these formed articles, films are widely used for magnetic recording media.
In the manufacture of polyester films, certain particles are dispersed in the polyester composition to provide an uneven surface and thereby improve the slipping property of the films lest that lacking of the slipping property should lead to a deterioration of productivity. For that reason, the technique for dispersing particles is a critical factor in the polyester composition for films.
Especially, those particles used in the polyester films for magnetic recording media are required not to form large projections or agglomerates on the surface of the films that may otherwise cause exfoliation of the material of the magnetic recording media. Thus the particles must have such excellent dispersability in the composition of polyester films for magnetic recording media as to prevent formation of agglomerates.
Besides, polyester films are ready to generate abrasion dusts or scratches on their surface when running during the manufacture or other processes. This causes, particularly in the case of polyester films for magnet recording media, a sudden deterioration of the performance and hence the quality of the magnet recording media.
From the viewpoint of the above problems, the polyester composition for films should meet the following requirements:
(1) The particles contained in the composition have not to form agglomerates; and
(2) The polyester composition has to guarantee excellent abrasion resistance and scratch resistance of the films produce therefrom.
In an attempt to improve the slipping property of the polyester film, for example, Japanese Patent Laid-Open (Sho) No. 60-179931 discloses a polyester film for magnetic tapes, which contains 0.01 to 1.0 wt. % of calcium carbonate particles with an average particle diameter of 0.01 to 0.39 xcexcm, and 0.005 to 0.2 wt. % of another calcium carbonate particles with an average particle diameter of 0.40 to 1.0 xcexcm.
Japanese Patent Laid-Open (Pyung) No. 2-214734 discloses a biaxially oriented polyester film with improved abrasion resistance and scratch resistance, which contains 0.1 to 2 wt. % of particles (A) with an average particle diameter of 5 to 400 nm, and 0.01 to 0.4 wt. % of particles (B) with an average particle diameter of 400 to 1,500 nm, the particles A and B being independently selected from the group consisting of xcex1-alumina, xcex3-alumina, xcex4-alumina, zirconia, titanium oxide, and organic polymers.
Japanese Patent Laid-Open (Pyung) No. 1-311131 discloses a polyester film with improved abrasion resistance and scratch resistance, which contains inert inorganic particles (A) with a Mohs hardness of more than 6 and inorganic particles (B) with an average particle diameter larger than that of the particles (A) and which exhibits an ultimate viscosity in the range from 0.52 to 0.62.
Further, Japanese Patent Laid-Open (Pyung) No. 8-134332 discloses a polyester film with improved abrasion resistance and scratch resistance which contains aluminum silicate particles and two additional particles (A) and (B), wherein particles (A) have a Mohs hardness of more than 6 and particles (B) have a Mohs hardness of less than 4.
In the light of recent tendencies of magnetic recording media, i.e., high recording density and high speed, the above-described conventional methods could not meet the requirements for quality of the films for magnetic recording media in regard to slipping property so that there is an increase in the risk of the generation of white powder to cause more frequent occurrence of dropout on the video tapes.
Especially, the larger quantity of particles in the composition, the more agglomeration of those which cause dropout on the video tapes, so it is strongly demanded to solve these problems.
To provide a polyester composition suitable for polyester films, the present invention uses aluminum silicate particles whose terminals are modified to enhance dispersability, abrasion resistance and scratch resistance, and further particles A with a Mohs hardness of more than 5 and particles B with a Mohs hardness of less than 4 to increase the abrasion resistance and scratch resistance of the polyester film.
It is therefore an object of the present invention to provide a polyester composition suitable for films lacking of large projections and excellent in both abrasion resistance and slipping property.
To achieve the above object, there is provided a polyester resin composition for films characterized in that the polyester composition comprises, based on 100 parts by weight of a polyester resin, 0.01 to 5 parts by weight of aluminum silicate particles containing aluminum and silica as principal components and an alkali metal.